Wireless networks enable communication with mobile devices, including those in ad-hoc networks. Wireless networks facilitate rapid field deployment, when compared to fixed wired networks. While wireless networks have their advantages, devices on wireless networks may consume a large amount of power during packet reception or while waiting to receive packets. Systems, methods, and devices that reduce power consumption may increase the time between battery charges and may reduce operational costs.
Communication standards incorporate power saving approaches to meet this need. For example, IEEE 802.11 power saving mode (PSM) defines two different power modes under which stations operate: active mode and regular power save (PS) mode. Stations in active mode may receive frames at any time. When in active mode, a station's primary receiver operates in an awake state, with sufficient power to receive frames.
Stations in regular PS mode may receive frames when their receivers are in an awake state. Stations in regular PS mode conserve power by transitioning to a lower power state (doze state) which usually consumes at least an order of magnitude less power than active state. When in doze state, the receiver does not operate with sufficient power to receive frames. In regular PS mode, all nodes in the network are synchronized to transition to wake up (transition to active state) to listen to beacon messages.
Broadcast, multicast or unicast messages to a power saving station are buffered at the transmitter and announced during the period when the nodes are in an awake state. The announcement is made using an ad hoc traffic indication message (ATIM) during a small time interval at the beginning of the beacon interval called the ATIM window. If a station receives a directed ATIM frame in the ATIM window, it sends an acknowledgement and stays awake for the entire beacon interval waiting for data packets to be transmitted. Immediately after the ATIM window, an access point can transmit buffered broadcast frames, multicast frames, data packets, and management frames addressed to stations that are known to be active based on previously received acknowledgements. Otherwise, the station may switch to the low-power doze state to conserve energy. In IEEE 802.11, a station's power management mode is indicated in the frame control field of the media access control header for each packet.
In regular PS mode, stations conserve power by transitioning to doze state most of the time, except for short intervals agreed with the transmitter when signals may be sent from the transmitter to the receiver. This is neither flexible nor efficient because in certain applications, the traffic pattern is unpredictable. The agreed awake time may not match the traffic pattern, so some awake times may not correspond to transmit times. There may also be times when transmitted signals are not received because they are transmitted outside of the agreed awake time.
Existing power save modes like 802.11 regular PS mode can be improved upon to further reduce power consumption. By further reducing power consumed by devices when waiting to receive packets or when receiving packets, power would be further conserved and operational costs further reduced.